During the inspection, repair and replacement of various components of an assembly, it may be necessary to remove one or more fasteners attaching a component to a mating structure. Unfortunately, certain fasteners may be difficult to remove due to the buildup of corrosion around the fastener hole which may bond or freeze the fastener in place over time. Sealants and coatings applied to the fastener after installation may also bond the fastener in place preventing removal of the fastener in a conventional manner using conventional tools.
For example, attempts to remove a machine screw that is frozen in place by engaging a screwdriver to a tool recess of the screw head may result in stripping out or deforming the tool recess and preventing further engagement thereof with the screwdriver. Attempts to remove a bolt that is frozen in place by engaging a box-end wrench or an open-end wrench to the bolt head may result in deforming or rounding off of the bolt head and eliminating the ability to further engage the wrench to the bolt head. In addition, attempts to remove a bolt that is frozen in place may result in shearing off of the bolt head at the surface of the structure leaving only the bolt shaft embedded in the structure.
Prior art solutions for removing frozen fasteners include the use of screw extractors which have sharpened flutes or teeth running along a length of the screw extractor. The teeth of such screw extractors are typically manually driven into an engagement hole that is drilled into the stripped fastener head or into the remaining shaft portion of the fastener. The engagement hole must be slightly smaller in diameter than the outer diameter of the screw extractor such that as the screw extractor is driven into the engagement hole, the teeth of the screw extractor can become sufficiently embedded into the inner diameter of the engagement hole. Once the screw extractor is sufficiently engaged to the engagement hole, a wrench or ratchet may be applied to a free end of the screw extractor and the fastener may be rotated and removed from the structure.
In order to avoid damage to the threaded bore into which the frozen fastener is installed, it is typically necessary that the engagement hole is generally aligned with the fastener. For example, for small diameter fasteners, to avoid drilling the engagement hole out of the side of the fastener shaft and damaging the threaded bore, the centerline of the engagement hole must be generally aligned with the centerline of the fastener. In addition, it is typically necessary that the engagement hole is centered on the fastener head or on the fastener shaft to avoid damage to the threaded bore.
A further requirement associated with the use of conventional screw extractors is that a sufficient amount of down force must be applied to the screw extractor in order to drive the screw extractor into the engagement hole such that the teeth of the screw extractor can become sufficiently embedded into the inner diameter. In this regard, incomplete or insufficient engagement of the screw extractor teeth into the engagement hole can result in stripping out of the engagement hole when rotating the screw extractor. Furthermore, in certain applications, it may be necessary to apply a down force to the screw extractor while simultaneously rotating the screw extractor during removal of the fastener to prevent the teeth of the screw extractor from becoming disengaged from the engagement hole which may result in stripping out the engagement hole.
The effectiveness of conventional screw extractors in removing frozen fasteners is dependent in part upon the skill of the operator both in forming the engagement hole in alignment with the fastener and in applying a sufficient amount of down force to engage the teeth of the screw extractor into the engagement hole. Performing such operations in the field adds complexity to the task and reduces the effectiveness of conventional screw extractors in removing certain fastener installations. For example, it may be necessary to remove a frozen fastener from an area that is difficult to access or which requires drilling an engagement hole in the fastener at an awkward angle. In addition, the fastener may be installed in a contoured surface making it difficult to determine the proper orientation for positioning a drill gun such that the drill bit is aligned with the fastener centerline.
As can be seen, there exists a need in the art for a system and method for removing a fastener that facilitates forming an engagement hole in a fastener and wherein the engagement hole is aligned with and centered on the fastener. Furthermore, there exists a need in the art for a system and method for removing a fastener wherein a sufficient amount of down force may be applied to the screw extractor in order to drive the screw extractor teeth into engagement with the engagement hole. Additionally, there exists a need in the art for a system and method for removing a fastener from a structure wherein the alignment of the screw extractor may be maintained while continuously applying a down force to the screw extractor during removal of the fastener. Finally, there exists a need in the art for a system and method for removing a fastener wherein the above-described alignment and down force requirements may be applied to fasteners installations in contoured surfaces.